Dummy Pixel ESD Protection in ToF Light Receiving Circuits
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Solution Overview
Problem
Conventional ToF-based distance measuring devices face challenges in ensuring adequate current for electrostatic discharge (ESD) surge protection without relying on the circuit configuration and size of the pixel circuit, particularly as miniaturization leads to reduced current capacity.
Innovation Solution
Incorporating a dummy pixel with a diode element connected in reverse polarity to the effective pixel's light receiving element, forming a surge current path in the dummy pixel region, which secures the necessary current for ESD surge protection without depending on the pixel circuit's configuration or size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a surge current path is provided in the pixel circuit for ESD protection, then the readout circuit is protected from ESD surge voltage, but the amount of current available for protection depends on the pixel circuit configuration and size, which limits protection capability in miniaturized devices
Solution Approach 1:
The invention divides the ESD protection function into two separate locations: the pixel circuit and the dummy pixel region. The pixel circuit contains a first diode for local protection, while the dummy pixel region contains a second diode that provides additional protection current. This segmentation allows the protection capability to be independent of the pixel circuit size.
Solution Approach 2:
The invention extends the ESD protection from a two-dimensional pixel circuit layout to a three-dimensional structure by utilizing the dummy pixel region as an additional spatial dimension. The second diode in the dummy pixel region provides protection current without occupying space within the pixel circuit itself, effectively adding a new dimension for protection current generation.
2Volume of moving object
If the pixel circuit is miniaturized to reduce device size, then the device becomes more compact, but the current capacity for ESD surge protection is reduced
Solution Approach 1:
The invention extracts the ESD protection current generation function from the pixel circuit by placing a second diode in the dummy pixel region. This extracted protection mechanism provides additional current capacity independent of the pixel circuit's miniaturization, allowing the device to be compact while maintaining adequate protection current capacity.
Solution Approach 2:
The dummy pixel region acts as an intermediary structure that mediates between the miniaturized pixel circuit and the ESD protection requirement. By placing the second diode in this intermediary region, the system achieves both compact size and adequate protection current capacity without direct conflict between the two requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for a larger current capacity for ESD surge protection, ensuring effective protection of the light receiving device and readout circuit without impacting the pixel circuit's functionality or size, even in miniaturized devices.
Implementation Method 1
a protection circuit including a diode element connected between a light receiving element of the dummy pixel and the second terminal in a polarity relationship in a reverse direction with respect to a light receiving element of the dummy pixel, and protecting a light receiving element of the effective pixel and a circuit element of the readout circuit from overvoltage
Implementation Method 2
a light receiving element that detects presence or absence of photons; the light receiving element of the effective pixel and the light receiving element of the dummy pixel may be avalanche diodes, for example, single photon avalanche diodes
Data Source
AI summary
ESD surge protection that does not depend on pixel circuits is disclosed. In one example, a light receiving device includes an effective pixel including a light receiving element that detects presence or absence of photons and a readout circuit that processes a signal output from the light receiving element. A first terminal applies a predetermined voltage to the light receiving element, a second terminal applies a first power supply voltage to the readout circuit, and a protection circuit protects a light receiving element and a circuit element of the readout circuit from overvoltage. The protection circuit includes a light receiving element of a dummy pixel connected to the first terminal, and a diode element connected to the light receiving element of the dummy pixel in a polarity relationship in a reverse direction between the light receiving element of the dummy pixel and the second terminal.